Cryogenic Cooling System

ABSTRACT

An improved cryogenic cooling system is disclosed. The cryogenic cooling system comprises a pressure sensing system disposed at or near the cryocooler to provide a more accurate representation of the pressure of the working gas within the cryocooler. By utilizing pressure measurements at the cryocooler, the thermal performance and net cooling capacity of the system may be improved. This may also improve the life of the cryocooler. Further, in some embodiments, pressure sensing systems are disposed at both the compressor and the cryocooler. In these embodiments, performance issues and potential failures may be monitored.

FIELD

This disclosure describes systems and method for controlling andmonitoring a cryogenic cooling system.

BACKGROUND

Cryogenic cooling systems are used to reduce the temperature of anenvironment to extremely low temperatures. Traditional closed loopgaseous cryogenic cooling systems are made up of two components; acompressor which is used to pressurize a working gas, and a cryocooler,which employs a refrigeration mechanism that uses the changing pressureof the working gas to extract heat from a system. In some embodiments,cryocoolers may be used in cryogenic vacuum pumps, which remove gassesfrom a vacuum chamber by condensing gasses in the vacuum chamber ontothe cold surfaces attached to the cryocooler.

In certain embodiments, the cryocooler operates using a Gifford-McMahoncycle. In a Gifford-McMahon cycle, a working gas at two differentpressures is utilized to perform heat exchange. The working gas in thesupply line may be at a first pressure, while the working gas in thereturn line may be at a second pressure, lower than the first pressure.In some embodiments, the pressure difference between the first pressureand the second pressure is directly related to the cooling ability ofthe cryocooler. In other words, a cryogenic pump achieves the desiredrefrigeration by the expansion of the working gas within the cryocooler.The cryocooler may include one or more stages. In embodiments where twostages are utilized, the temperature in the first stage may be between50K and 80K and the temperature in the second stage may be lower, suchas between 10K and 20K. In embodiments where a single stage is utilized,the temperature may be as low as 40K.

Further, in certain embodiments, the compressor and the cryocooler maybe physically located very close to one another. However, in otherembodiments, the compressor and the cryocooler may be physicallyseparated, such as by 10 meters or more. Additionally, in certainembodiments, the compressor may be used to provide pressurized gas to aplurality of cryocoolers.

Consequently, in certain embodiments, it is possible that the pressureof the working gas at the cryocooler is different than the pressure ofthe working gas at the compressor. This difference may affect theperformance of the cryocooler.

Therefore, it would be advantageous if there were a system and methodthat improved cryocooler performance and net cooling capacity. Further,it would be beneficial if this system allowed the cryocooler andcompressor to be physically separate with no degradation in performance.

SUMMARY

An improved cryogenic cooling system is disclosed. The cryogenic coolingsystem comprises a pressure sensing system disposed at or near thecryocooler to provide a more accurate representation of the pressure ofthe working gas within the cryocooler. By utilizing pressuremeasurements at the cryocooler, the thermal performance, net coolingcapacity and/or efficiency of the cooling system may be improved. Thismay also improve the life of the cryocooler. Further, in someembodiments, pressure sensing systems are disposed at both thecompressor and the cryocooler. In these embodiments, performance issuesand potential failures may be monitored.

According to one embodiment, a cryogenic cooling system is disclosed.The cryogenic cooling system comprises a compressor; a cryocooler; asupply conduit and a return conduit connecting the compressor and thecryocooler; and a first pressure sensing system disposed at or proximatethe cryocooler to measure at least one of: differential pressure betweenthe supply conduit and the return conduit; pressure of the supplyconduit; pressure of the return conduit. In certain embodiments, thecryogenic cooling system comprises a controller in communication withthe first pressure sensing system. In some embodiments, the firstpressure sensing system measures differential pressure between thesupply conduit and the return conduit at or proximate the cryocooler. Incertain embodiments, the compressor is regulated based on thedifferential pressure between the supply conduit and the return conduitmeasured at or proximate the cryocooler. In some embodiments, thecontroller detects impending failures in the cryocooler based on thedifferential pressure between the supply conduit and the return conduitat or proximate the cryocooler. In certain embodiments, the controllermonitors the differential pressure over time to detect impendingfailures. In some embodiments, the controller monitors the differentialpressure over time, creates a pressure vs. time curve and compares thepressure vs. time curve to a library of curves that represent differentfailure modes. In some embodiments, the cryogenic cooling systemcomprises a flow rate sensor to measure a flow rate of working gas inthe supply conduit or the return conduit, and wherein the flow rate isused in conjunction with the differential pressure to detect animpending failure. In certain embodiments, the cryogenic cooling systemcomprises comprising a second cryocooler in communication with thesupply conduit and the return conduit and having a first pressuresensing system disposed at or proximate the second cryocooler to measureat least one of: differential pressure between the supply conduit andthe return conduit; pressure of the supply conduit; and pressure of thereturn conduit. In some embodiments, the compressor is regulated toachieve a minimum differential pressure between the supply conduit andthe return conduit measured at or proximate the cryocooler and measuredat or proximate the second cryocooler. In certain embodiments, thecryocooler comprises a valving system in communication with the supplyconduit, the return conduit and a cylinder within the cryocooler, andwherein the first pressure sensing system comprises a pressure sensor incommunication with the cylinder, such that the pressure sensor measuresthe pressure within the supply conduit or the return conduit, based on astate of the valving system.

According to another embodiment, a cryogenic cooling system isdisclosed. The cryogenic cooling system comprises a compressor; acryocooler; a supply conduit and a return conduit connecting thecompressor and the cryocooler; a first pressure sensing system disposedat or proximate the cryocooler to measure at least one of: differentialpressure between the supply conduit and the return conduit; pressure ofthe supply conduit; and pressure of the return conduit; and a secondpressure sensing system disposed at or proximate the compressor tomeasure at least one of: differential pressure between the supplyconduit and the return conduit; pressure of the supply conduit; andpressure of the return conduit. In certain embodiments, the cryogeniccooling system comprises a controller in communication with the firstpressure sensing system and the second pressure sensing system. Incertain embodiments, the first pressure sensing system and the secondsensing system measure differential pressure between the supply conduitand the return conduit. In some embodiments, the controller estimates apressure drop through the supply conduit or return conduit based on thedifferential pressure measured by the first pressure sensing system andthe second pressure sensing system. In certain embodiments, thecontroller performs an action if the pressure drop through the supplyconduit or return conduit is greater than a predetermined value. Incertain embodiments, the pressure drop through the supply conduit orreturn conduit is determined based on measurements from the firstpressure sensing system and the second pressure sensing system. Incertain embodiments, the controller performs an action if the pressuredrop through the supply conduit or return conduit is greater than apredetermined value. In certain embodiments, the controller monitors thepressure drop over time, creates a pressure vs. time curve and comparesthe pressure vs. time curve to a library of curves that representdifferent failure modes.

According to another embodiment, an ion implantation system isdisclosed. The ion implantation system comprises an ion source togenerate an ion beam; a processing chamber comprising a platen on whicha workpiece may be disposed; beam line components to guide the ion beamfrom the ion source to the processing chamber; and a cryogenic coolingsystem in communication with the processing chamber, wherein thecryogenic cooling system comprises: a compressor; a cryocooler; a supplyconduit and a return conduit connecting the compressor and thecryocooler; and a first pressure sensing system disposed at or proximatethe cryocooler to measure at least one of: differential pressure betweenthe supply conduit and the return conduit; pressure of the supplyconduit; and pressure of the return conduit.

BRIEF DESCRIPTION OF THE FIGURES

For a better understanding of the present disclosure, reference is madeto the accompanying drawings, which are incorporated herein by referenceand in which:

FIG. 1 shows a cryogenic cooling system according to one embodiment;

FIG. 2 shows a P-V graph indicative of the operation of the cryocooler;and

FIG. 3 shows a cryogenic cooling system according to another embodiment;

FIG. 4 shows a cryogenic cooling system with multiple cryocoolersaccording to another embodiment; and

FIG. 5 shows an ion implantation system that utilizes the cryogeniccooling system described herein.

DETAILED DESCRIPTION

The present disclosure describes an improved cryogenic cooling system.FIG. 1 shows this improved cryogenic cooling system according to a firstembodiment. The cryogenic cooling system 10 comprises two maincomponents; a compressor 20 and a cryocooler 50.

A supply conduit 30 and a return conduit 40 are in fluid communicationwith the compressor 20 and the cryocooler 50.

The compressor 20 is used to pressurize a working gas, such as helium orhydrogen, to a first pressure. In certain embodiments, the firstpressure may be 400 psi or more. This working gas at the first pressureis directed through the supply conduit 30 toward the cryocooler 50.After exiting the cryocooler 50, the working gas in the return conduit40 may be a pressure that is less than the first pressure, such as 200psi. In certain embodiments, the compressor 20 attempts to maintain adifferential pressure between the working gas in the supply conduit 30and the working gas in the return conduit 40.

In certain embodiments, one or more couplings 35 may be used to attachthe supply conduit 30 to the compressor 20 and the cryocooler 50.Additionally, though not shown, couplings 35 may be used to attachsegments of conduit together to create a supply conduit 30 of thedesired length. Similarly, one or more couplings 45 may be used toattach the return conduit 40 to the compressor 20 and the cryocooler 50.Additionally, though not shown, couplings 45 may be used to attachsegments of conduit together to create a return conduit 40 of thedesired length.

As shown in FIG. 1 , the cryocooler 50 comprises a movable displacer 55disposed in a cylinder 60. The movable displacer 55 is driven by a motor90. The motor 90 may be electric or pneumatic. In certain embodiments,the motor 90 may exist within the working gas volume and include adisplacer drive seal 91. The connection between the motor 90 and themovable displacer 55 may exist within the volume of the return path.Thus, to prevent the working gas from flowing directly from the supplyconduit 30 to the return conduit 40, displacer drive seals 91 areutilized. The cryocooler 50 also comprises a valving system 70 such thateither the working gas from the supply conduit 30 is in fluidcommunication with the cylinder 60, or the working gas from the returnconduit 40 is in fluid communication with the cylinder 60. The valvingsystem 70 may comprise two separate valves 71, as shown in FIGS. 1 and 3, or may comprise a single valve that selects between the supply conduit30 and the return conduit 40.

Additionally, a regenerator material 65 may be disposed in thecryocooler 50 along the path through which the working gas travels. Incertain embodiments, the regenerator material 65 may be disposed in thecylinder 60, or in the movable displacer 55.

In certain embodiments, a second and/or third stage may be employed,featuring additional volumes and displacers mechanically tied togetherto provide the system the ability to achieve lower temperatures.

Next, the operation of the cryocooler 50 will be described in referenceto FIG. 1 and FIG. 2 , which illustrates the changes in the pressure andvolume of the working gas during the cycle.

In operation, the valving system 70 is first configured to allow workinggas from the supply conduit 30 to enter the cylinder 60. At this time,the movable displacer 55 may be at or near the first position where thedisplaced volume 62 in the cylinder 60 is at or near a minimum. This isshown as point 105 in FIG. 2 . As working gas from the supply conduit 30enters the cylinder 60, it passes through the regenerator material 65,losing heat to the regenerator material 65. The working gas causes thepressure within the cylinder 60 and displaced volume 62 to increase, asshown in line 110, until it reaches a state where the pressure is at ornear the pressure of the supply conduit 30 and the volume is at or neara minimum volume, as shown in point 120.

Also, at this time, the movable displacer 55 moves so as to expand thedisplaced volume 62. Thus, the volume in the displaced volume 62increases while pressure stays roughly constant. This change in volumeis shown in line 130 in FIG. 2 . The movable displacer 55 reaches thesecond position where the displaced volume 62 is at or near a maximum,designated at point 140 in FIG. 2 . At or near this time, the valvingsystem 70 switches to allow the cylinder 60 to be in fluid communicationwith the return conduit 40. The change in pressure within the cylinder60 causes a decrease in temperature, which results in cooling. Thischange in pressure is shown in line 150 of FIG. 2 and results in thestate shown at point 160. As the working gas exits the cylinder 60, itpasses through the regenerator material 65, which loses its heat to theworking gas. While the valving system 70 remains in this position, themovable displacer 55 moves toward the first position, reducing thedisplaced volume 62. This change in volume is shown in line 170 andresult in the state shown at point 105. The process then repeats.

The amount of cooling may be related to the area enclosed in the graphshown in FIG. 2 . The amount of cooling is also related to the frequencyof the movable displacer 55, which determines how often the cycle shownin FIG. 2 is executed. Given that the maximum volume of displaced volume62 is fixed, the amount of cooling is most affected by the difference inpressure between the supply conduit 30 and the return conduit 40, andthe frequency of the movable displacer 55.

Thus, in one embodiment, a first pressure sensing system 80 may bedisposed at or near the cryocooler 50. In certain embodiments, thecryocooler 50 may include manifolding 51 within the cryocooler assembly,and the first pressure sensing system 80 may be disposed in themanifolding 51. In another embodiment, the first pressure sensing system80 may be disposed at the couplings that are used to attach thecryocooler 50 to the supply conduit 30 and the return conduit 40. Inanother embodiment the sensors may be integrated into the valving system70. In yet another embodiment, multiple cryocoolers 50 may be disposednear one another with shared manifolding and the first pressure sensingsystem 80 may be disposed at the shared manifolding. In each embodiment,the first pressure sensing system 80 is disposed as close as practicalto the cryocooler 50. In certain embodiments, the first pressure sensingsystem 80 may be disposed at the coupling between the conduits and thecryocooler 50 or even closer to the cryocooler 50, and optionally withinthe cryocooler 50. Thus, as used in this disclosure, the phrase “at orproximate the cryocooler” is intended to denote any configuration wherethe first pressure sensing system 80 is disposed within the cryocooler50, in the manifolding 51 of the cryocooler 50, or at the attachmentpoints for the supply conduit 30 and the return conduit 40. In anotherembodiment, shown in FIG. 3 , the first pressure sensing system 80 maybe in fluid communication with the warmer end of the cylinder 60.

In one embodiment, the first pressure sensing system 80 comprises adifferential pressure sensor adapted to measure the difference inpressure between the supply conduit 30 and the return conduit 40 at ornear the entrance to the cryocooler 50. In another embodiment, the firstpressure sensing system 80 may comprise two pressure sensors, one tomeasure the pressure of each conduit. The pressure sensors may measureabsolute pressure (i.e. the pressure relative to vacuum) or gaugepressure (i.e. the pressure relative to atmospheric pressure).Throughout this disclosure, the term “pressure” is meant to denoteabsolute pressure or gauge pressure, as distinguished from differentialpressure.

In the embodiment shown in FIG. 3 , a single pressure sensor may be influid communication with the cylinder 60, such as the warmer end of thecylinder 60. This pressure sensor may be used to measure the pressurewithin the cylinder 60 while the supply valve or return valve is open totheir respective conduit. In this way, a single pressure sensor may beused to monitor both the pressure within the supply conduit 30 and thereturn conduit 40, based on the state of the valving system 70.

The output or outputs from the first pressure sensing system 80 mayserve as inputs to a controller 100. The controller 100 may include aprocessing unit, such as a microcontroller, a personal computer, aspecial purpose controller, or another suitable processing unit. Thecontroller 100 may also include a non-transitory storage element, suchas a semiconductor memory, a magnetic memory, or another suitablememory. This non-transitory storage element may contain instructions andother data that allows the controller 100 to perform the functionsdescribed herein.

For example, the controller 100 may be used to control the compressor20, so as to maintain the desired pressure differential at thecryocooler 50. While the controller 100 is shown as being external tothe compressor 20, in some embodiments, the controller 100 may beintegrated into the compressor 20 or the cryocooler 50.

Thus, according to one embodiment, a first pressure sensing system 80 isused in conjunction with a controller 100 to regulate the compressor 20so as to maintain a desired pressure difference between the supplyconduit 30 and the return conduit 40 at or near the cryocooler 50. Inaddition, the controller 100 may also control the frequency of themovable displacer 55 so as to achieve the desired temperature on thecold end 61 of the cryocooler 50.

In certain embodiments, the compressor 20 may include a second pressuresensing system 21. In some embodiments, the second pressure sensingsystem 21 may be a differential pressure sensor, that measures thepressure difference between the supply conduit 30 and the return conduit40 at or near the entrance and exit from the compressor 20. In certainembodiments, the differential pressure sensor may measure the pressuredifference between the point of connection of the return conduit 40 anda location between the compressor pump and the adsorber within thecompressor 20. In another embodiment, the second pressure sensing system21 may comprise two pressure sensors, one to measure the pressure ofeach conduit at or near the entrance and exit from the compressor 20. Inyet another embodiment, the second pressure sensing system 21 maycomprise one pressure sensor to measure the pressure of the supplyconduit 30 at or near the exit from the compressor 20. Thus, as used inthis disclosure, the phrase “at or proximate the compressor” is intendedto denote any configuration where the second pressure sensing system 21is disposed within the compressor 20, or at the attachment points forthe supply conduit 30 and the return conduit 40.

If both pressure sensor systems comprise differential pressure sensors,the controller 100 may receive two inputs; the differential pressure ator near the compressor 20 from the second pressure sensing system 21,and the differential pressure at or near the cryocooler 50 from thefirst pressure sensing system 80. The controller 100 may then estimatethe pressure drop through the supply conduit 30 and the return conduit40. For example, if the pressure differential at the compressor 20 is200 psi, and the pressure differential at the cryocooler 50 is 180 psi,the controller 100 may assume that the pressure drop through eachconduit is equal and therefore each conduit represents a pressure dropof 10 psi.

In certain embodiments, both pressure sensor systems comprise at leasttwo pressure sensors; a first to measure the pressure of the supplyconduit 30 and a second to measure the return conduit 40. In theseembodiments, the controller 100 may receive at least four inputs and maydirectly calculate the pressure drop through each conduit.

In certain embodiments, the second pressure sensing system 21 allows apressure sensing of either the supply conduit 30 or the return conduit40. In these embodiments, the first pressure sensing system 80 maycomprise at least one pressure sensor to measure the pressure of thesame conduit at or near the cryocooler 50. This configuration allows thecontroller 100 to receive pressure readings from both ends of one of theconduits and calculate the pressure drop through the conduit. Thecontroller 100 may then estimate that the pressure drop through theother conduit is roughly equal to the calculated pressure drop.

Thus, in each of these embodiments, the controller 100 may be able todetermine or estimate the pressure drop through the supply conduit 30and the return conduit 40. In doing so, the controller 100 may be betterable to control and monitor the cryogenic cooling system 10.

For example, as stated above, in one embodiment, the compressor 20 iscontrolled based on the pressure differential measured at or near thecryocooler 50. This improves the net cooling capacity of the cryocooler50. For example, as stated above, the cooling is a function of thepressure differential, the displaced volume and the frequency of themovable displacer 55.

Net cooling (Q) may be represented as:

Q=f*ΔP*V,

where f is the frequency of the movable displacer 55, V is the displacedvolume 62, and ΔP is the difference in pressure between the supplyconduit 30 and the return conduit 40, as seen by the cryocooler 50.

Thus, if the pressure differential is controlled based on measurementsmade at the cryocooler 50, as opposed to measurements made at thecompressor 20, the pressure differential may be higher. Consequently, toachieve the same cooling, the frequency of the movable displacer 55 maybe reduced. Also, the system may vary the pressure at the cryocooler 50so as to cause the reciprocating frequency of the compressor 20 to beoptimized for higher or lower heat loads.

In certain embodiments, the first pressure sensing system 80 is used inconjunction with the second pressure sensing system 21 to regulate thecompressor 20. For example, the controller 100 may use the values fromthe first pressure sensing system 80 to control the compressor 20, butmay also use the second pressure sensing system as a backup or afailover system.

Additionally, the first pressure sensing system 80 may be used tomonitor and diagnose performance issues in the cryocooler 50. Forexample, a differential pressure drop outside an expected range ofvalues may be indicative of an impending failure. For example, incertain embodiments, an application specific threshold may be adopted.In one embodiment, this application specific threshold may be a drop inthe differential pressure of greater than 10%. Specifically, anunexpected differential pressure may be indicative of a leak within thecylinder 60, such as a faulty displacer drive seal 91 or faulty valve 71within valving system 70. Alternatively, an unexpected differentialpressure may be indicative that the working gas is flowing directly fromthe supply conduit 30 to the return conduit 40, a condition referred toas blow-by. Additionally, an unexpected differential pressure may beindicative of clogging of the movable displacer 55. Thus, in certainembodiments, the controller 100 may take an action upon detecting adifferential pressure that is outside an expected range of values.

Furthermore, providing pressure sensing at the cryocooler 50, inaddition to pressure sensing at the compressor 20 has otherapplications. As described above, by utilizing a first pressure sensingsystem 80 and a second pressure sensing system 21, it is possible forthe controller 100 to determine or estimate the pressure drop througheach conduit.

For example, if the controller detects a large pressure drop through oneor both of the conduits, this may be indicative of an issue with theconduits. In certain embodiments, a pressure drop of more than apredetermined threshold may be indicative of an issue. In someembodiments, that predetermined threshold may be more than 10 PSI andmay be adjusted for installation specific geometry such as line length,line diameter, line material, and number of couplings. For example, akink or obstruction in a conduit would result in a large pressure dropthrough the conduit. Additionally, an incorrectly installed coupling maycause such a large pressure drop due to the self sealing refrigerantfittings not opening completely. Additionally, a conduit of excessivelength may result in a large pressure drop.

In certain embodiments, a flow rate sensor 37 may be incorporated intothe cryogenic cooling system 10. For example, a flow rate sensor 37 maybe disposed to measure the flow rate of the working gas in the supplyconduit 30 or the return conduit 40. In other embodiments, the flow ratesensor 37 may be disposed in the cryocooler 50 or compressor 20.

Thus, in certain embodiments, the controller 100 may utilize the firstpressure sensing system 80 and the second pressure sensing system 21 inconjunction with other operating parameters such as the flow rate of theworking gas, as measured by the flow rate sensor 37, to determine aspecific mode of failure. For example, a high flow with a smalldifferential pressure may be indicative of a condition where the workinggas is bypassing the displacer drive seals 91 or any combination of thevalves 71 within the valving system 70.

Additionally, the first pressure sensing system 80 and the secondpressure sensing system 21 may be utilized with the controller 100 togenerate pressure vs time curves for either the differential pressure orthe pressure at the cryocooler 50, the supply conduit 30 or returnconduit 40. The controller 100 may compare these pressure vs time curvesto a library of identified failure mode curves for the purpose ofdiagnostics. In one example, the controller 100 may detect a subtlechange in differential pressure or pressure at the supply or return thatoccurs over time. This may be indicative of a failing or clogged valve71 in the valving system 70. Alternatively, this may be indicative of afailing displacer drive seal 91.

Alternatively, a simpler approach of monitoring for a change in pressureover a particular time period may be employed.

Thus, in some embodiments, the controller 100 measures or estimates thepressure drop through the supply conduit 30 and/or the return conduit40, and performs an action if the pressure drop exceeds a predeterminedvalue.

The actions described above may take many forms. In one embodiment, theaction may comprise an alert to an operator. This alert may be visual,such as a warning light, a message on a display unit, a message over acommunication path to a host control system, a signal relay or similarelement to signal a failure to the host control system or anotherelectronic, fiber optic, or pneumatic means of communicating with a hostcontrol system. Alternatively, the alert may be audio, such as a warningtone. In another embodiment, the action may be to disable the compressor20 and/or the cryocooler 50 until the issue has been addressed.

FIG. 4 shows another embodiment. In this embodiment, the compressor 20is used to supply working gas to multiple cryocoolers 50. A firstpressure sensing system 80 is disposed at or near each cryocooler 50.The outputs from each of these first pressure sensing systems 80 is incommunication with the controller 100. By having visibility to differentfirst pressure sensing systems 80, the controller 100 is better able tomonitor the activities of each cryocooler 50. For example, thecontroller 100 may regulate the compressor 20 such that the differentialpressure at each cryocooler 50 is at least a predetermined minimumvalue. In this way, each cryocooler 50 is ensured to have a pressuredifferential that is equal to or greater than some predeterminedminimum.

In addition, by having access to the pressure at the various cryocoolers50, the controller 100 may be able to detect anomalies or other issues.For example, if the pressure (either differential, gauge or absolute) atone of the cryocoolers 50 is significantly different from the pressureat the other cryocoolers 50, this may signify one of the issuesdescribed above. Thus, the controller 100 may initiate an action if thepressure at one or more of the cryocoolers 50 is different from thepressure at other cryocoolers by more than a predetermined value.

The cryocooling system described herein may be used as a cryogenic pumpin an ion implantation system. FIG. 5 shows a representativeillustration of an ion implantation system that utilizes the cryogeniccooling system described here.

The ion implantation system includes an ion source 500. In certainembodiments, the ion source 500 may be an RF ion source. In anotherembodiment, the ion source 500 may be an indirectly heated cathode(IHC). Other embodiments are also possible. For example, the plasma maybe generated in a different manner, such as by a Bernas ion source, acapacitively coupled plasma (CCP) source, microwave or ECR(electron-cyclotron-resonance) ion source. The manner in which the ionsis generated is not limited by this disclosure.

One chamber wall, referred to as the extraction plate, includes anextraction aperture. The extraction aperture may be an opening throughwhich the ions generated in the ion source chamber are extracted anddirected toward a workpiece 510. The extraction aperture may be anysuitable shape. In certain embodiments, the extraction aperture may beoval or rectangular shaped, having one dimension, referred to as thewidth (x-dimension), which may be much larger than the second dimension,referred to as the height (y-dimension). In certain embodiments, aribbon ion beam is extracted from the ion source 500. In otherembodiments, a spot ion beam is extracted from the ion source 500.

Disposed outside and proximate the extraction aperture of the ion source500 are extraction optics 503. In certain embodiments, the extractionoptics 503 comprises one or more electrodes. Each electrode may be asingle electrically conductive component with an aperture disposedtherein. Alternatively, each electrode may be comprised of twoelectrically conductive components that are spaced apart so as to createthe aperture between the two components. The electrodes may be a metal,such as tungsten, molybdenum or titanium. One or more of the electrodesmay be electrically connected to ground. In certain embodiments, one ormore of the electrodes may be biased using an extraction power supply.The extraction power supply may be used to bias one or more of theelectrodes relative to the ion source 500 so as to attract ions throughthe extraction aperture.

Located downstream from the extraction optics 503 is a mass analyzer520. The mass analyzer 520 uses magnetic fields to guide the path of theextracted ions. The magnetic fields affect the flight path of ionsaccording to their mass and charge. A mass resolving device 521 that hasa resolving aperture 522 is disposed at the output, or distal end, ofthe mass analyzer 520.

By proper selection of the magnetic fields, only those ions that have aselected mass and charge will be directed through the resolving aperture522. Other ions will strike the mass resolving device 521 or a wall ofthe mass analyzer 520 and will not travel any further in the system.

A collimator 585 is disposed downstream from the mass resolving device521. The collimator 585 accepts the ions that pass through the resolvingaperture 522 and creates a ribbon ion beam formed of a plurality ofparallel or nearly parallel beamlets.

The extraction optics 503, the mass analyzer 520, the mass resolvingdevice 521, and the collimator 585 may be considered beam linecomponents that guide the ion beam from the ion source 500 to theprocessing chamber 590. Of course, the ion implantation system mayinclude other beamline components, such as a scanner to create a ribbonbeam from a spot ion beam, and additional electrodes to accelerate ordecelerate the beam and other elements.

The final ion beam 555 impacts the workpiece 510 disposed on the platen560 within a processing chamber 590. The processing chamber 590 may bemaintained at near vacuum conditions, which may be less than 100 mTorr.In certain embodiments, the processing chamber 590 is maintained at lessthan 10 mTorr. In certain embodiments, the processing chamber 590 ismaintained at less than 1E-4 Torr. The pressure within the processingchamber 590 may be such that the mean free path of molecules within theprocessing chamber 590 is at least greater than the dimension of theprocessing chamber 590. This may be achieved through the use of one ormore cryogenic cooling systems 10 that are in communication with theprocessing chamber 590 and act as cryogenic pumps.

Thus, the cryogenic cooling systems described herein may be applied toion implantation systems to create near vacuum conditions within aprocessing chamber.

The system described herein has many advantages. First, as describedabove, by regulating the compressor 20 to deliver the desireddifferential pressure at the cryocooler 50, it may be possible to reducethe frequency of the movable displacer 55. This may increase the life ofthe cryocooler 50, by reducing wear of internal seals, valves 71, motor90, and/or rotary to linear translation mechanisms, such as scotchyokes.

Second, by having visibility to the differential pressure at thecryocooler 50, it may be possible for the controller 100 to identifyissues, such as blow-by, failed valves 71, ruptured or worn seals,clogged compressor adsorber(s) and clogged displacers. In response, thecontroller 100 may initiate an action which allows the operator toaddress the issue in a timely manner.

Third, by having visibility to the pressure at both ends of the supplyconduit 30 and/or return conduit 40, it is possible for the controller100 to determine the pressure drop through the conduits. An unexpectedlyhigh pressure drop may be indicative of an issue, such as an improperlyinstalled coupling, a kink or obstruction in the conduit, or cloggedcompressor adsorber. In response, the controller may initiate an actionwhich allows the operator to address the issue in a timely manner.

The present disclosure is not to be limited in scope by the specificembodiments described herein. Indeed, other various embodiments of andmodifications to the present disclosure, in addition to those describedherein, will be apparent to those of ordinary skill in the art from theforegoing description and accompanying drawings. Thus, such otherembodiments and modifications are intended to fall within the scope ofthe present disclosure. Furthermore, although the present disclosure hasbeen described herein in the context of a particular implementation in aparticular environment for a particular purpose, those of ordinary skillin the art will recognize that its usefulness is not limited thereto andthat the present disclosure may be beneficially implemented in anynumber of environments for any number of purposes. Accordingly, theclaims set forth below should be construed in view of the full breadthand spirit of the present disclosure as described herein.

What is claimed is:
 1. A cryogenic cooling system, comprising: acompressor; a cryocooler; a supply conduit and a return conduitconnecting the compressor and the cryocooler; and a first pressuresensing system disposed at or proximate the cryocooler to measure atleast one of: differential pressure between the supply conduit and thereturn conduit; pressure of the supply conduit; and pressure of thereturn conduit.
 2. The cryogenic cooling system of claim 1, furthercomprising a controller in communication with the first pressure sensingsystem.
 3. The cryogenic cooling system of claim 2, wherein the firstpressure sensing system measures differential pressure between thesupply conduit and the return conduit at or proximate the cryocooler. 4.The cryogenic cooling system of claim 3, wherein the compressor isregulated based on the differential pressure between the supply conduitand the return conduit measured at or proximate the cryocooler.
 5. Thecryogenic cooling system of claim 3, wherein the controller detectsimpending failures in the cryocooler based on the differential pressurebetween the supply conduit and the return conduit at or proximate thecryocooler.
 6. The cryogenic cooling system of claim 5, wherein thecontroller monitors the differential pressure over time to detectimpending failures.
 7. The cryogenic cooling system of claim 5, whereinthe controller monitors the differential pressure over time, creates apressure vs. time curve and compares the pressure vs. time curve to alibrary of curves that represent different failure modes.
 8. Thecryogenic cooling system of claim 5, further comprising a flow ratesensor to measure a flow rate of working gas in the supply conduit orthe return conduit, and wherein the flow rate is used in conjunctionwith the differential pressure to detect an impending failure.
 9. Thecryogenic cooling system of claim 2, further comprising a secondcryocooler in communication with the supply conduit and the returnconduit and having a first pressure sensing system disposed at orproximate the second cryocooler to measure at least one of: differentialpressure between the supply conduit and the return conduit; pressure ofthe supply conduit; and pressure of the return conduit.
 10. Thecryogenic cooling system of claim 9, wherein the compressor is regulatedto achieve a minimum differential pressure between the supply conduitand the return conduit measured at or proximate the cryocooler andmeasured at or proximate the second cryocooler.
 11. The cryogeniccooling system of claim 1, wherein the cryocooler comprises a valvingsystem in communication with the supply conduit, the return conduit anda cylinder within the cryocooler, and wherein the first pressure sensingsystem comprises a pressure sensor in communication with the cylinder,such that the pressure sensor measures the pressure within the supplyconduit or the return conduit, based on a state of the valving system.12. A cryogenic cooling system, comprising: a compressor; a cryocooler;a supply conduit and a return conduit connecting the compressor and thecryocooler; a first pressure sensing system disposed at or proximate thecryocooler to measure at least one of: differential pressure between thesupply conduit and the return conduit; pressure of the supply conduit;and pressure of the return conduit; and a second pressure sensing systemdisposed at or proximate the compressor to measure at least one of:differential pressure between the supply conduit and the return conduit;pressure of the supply conduit; and pressure of the return conduit. 13.The cryogenic cooling system of claim 12, further comprising acontroller in communication with the first pressure sensing system andthe second pressure sensing system.
 14. The cryogenic cooling system ofclaim 13, wherein the first pressure sensing system and the secondsensing system measure differential pressure between the supply conduitand the return conduit.
 15. The cryogenic cooling system of claim 14,wherein the controller estimates a pressure drop through the supplyconduit or return conduit based on the differential pressure measured bythe first pressure sensing system and the second pressure sensingsystem.
 16. The cryogenic cooling system of claim 15, wherein thecontroller performs an action if the pressure drop through the supplyconduit or return conduit is greater than a predetermined value.
 17. Thecryogenic cooling system of claim 13, wherein a pressure drop throughthe supply conduit or return conduit is determined based on measurementsfrom the first pressure sensing system and the second pressure sensingsystem.
 18. The cryogenic cooling system of claim 17, wherein thecontroller performs an action if the pressure drop through the supplyconduit or return conduit is greater than a predetermined value.
 19. Thecryogenic cooling system of claim 17, wherein the controller monitorsthe pressure drop over time, creates a pressure vs. time curve andcompares the pressure vs. time curve to a library of curves thatrepresent different failure modes.
 20. An ion implantation systemcomprising: an ion source to generate an ion beam; a processing chambercomprising a platen on which a workpiece may be disposed; beam linecomponents to guide the ion beam from the ion source to the processingchamber; and a cryogenic cooling system in communication with theprocessing chamber, wherein the cryogenic cooling system comprises: acompressor; a cryocooler; a supply conduit and a return conduitconnecting the compressor and the cryocooler; and a first pressuresensing system disposed at or proximate the cryocooler to measure atleast one of: differential pressure between the supply conduit and thereturn conduit; pressure of the supply conduit; and pressure of thereturn conduit.